This book begins with the death of the Duchess Elizabeth Renata, and the events making up the plot are influenced by this event.
This book starts off slowly, introducing the Austrian Habsburgs, Duke Maxamillian II of Bavaria, and Duke Ernst of Saxe-Weimar. It proceeds rather calmly for several hundred pages handling setup, and describing events that are of little interest later in the book. Things pick up after Veronica Dreeson and Mary Simpson are kidnapped by a panicked pair of amateur spies. They are then taken to Bavaria and become a catalyst for more trouble in Bavaria.
I enjoyed this book. It is significantly more focused then "1633" and includes several vibrant characters. Maria Anna is particularly vivid. The plots and politics are well described. This book is well worth reading if you find Eric Flint's project in alternate history fascinating. If you aren't interested this book is not as strong a stand alone novel as others in the series.